1. Field of the Invention
The present invention pertains to movable irrigation systems, and more particularly, to relatively large irrigation systems which are arranged to be connected to a fixed water supply and to move about the water supply under power supplied by the pressure from the water supply.
2. Description of the Prior Art
Typical irrigation systems include a ditch and furrow type of irrigation system, a flooding type of irrigation system and a sprinkling type of irrigation system. The flooding type and the ditch and furrow type of irrigation systems may be used where the fields are relatively level or have a general slope. The sprinkling type of irrigation may be used with land which does not lend itself to the other types of irrigation or wherein the cost of other systems is relatively high. Sprinkling also has the advantage of having less crusting of the soil, and, as a result the water soaks into the soil faster and results in less evaporation of water than where flooding is used. In many areas of the world the sprinkling system is less expensive to build and operate than the other types of irrigation systems.
Typically the sprinkling systems a string of interconnected pipe sections having sprinkler heads, or other water spreading means, arranged at spaced intervals along the length thereof and with support wheels being provided for the pipe sections at generally uniformly spaced intervals along the length of the pipe. The wheels may be arranged to support the pipe sections so that they pass through the axis of the wheels, or the wheels may be mounted on carriages for supporting the pipe sections at an offset position. In either case, the pipe sections and their associated sprinkler heads are supported at a fixed distance above the ground so that they will be above the crop which is to be irrigated. Some means is typically provided to move the string of pipe sections along the area to be sprinkled with the wheels rolling along in predetermined tracks. This movement can be either linear or it can be rotary, i.e., the pipe string can rotate about a central pivot axis where an upstanding water supply pipe is located to which one end of the pipe string is attached.
In the rotary movement type of irrigation system, the interconnected string of pipe sections extends radially from the water supply pipe and is driven either by means of the carriages which support the pipe sections at spaced intervals or by means of a single power mover connected to the string of pipe sections at or near the outer end thereof. The power for the single power mover means may be provided by an electric battery, a gasoline driven engine, or through an electrical power line running along the length of the irrigation tubing and connected to an electrical outlet at the inner, fixed end thereof. Alternately, the power mover may be powered directly through the water pressure in the pipe sections.
The water driven irrigation system has the obvious advantage of not requiring a separate power source to move the pipe over the irrigation area. Such a system has found to be workable as the drive means can be geared to operate at a very low ground speed so that the total area being irrigated will be provided with sufficient water. Typically, the string of interconnected pipe sections makes one complete revolution in the time normally required between waterings (about eight days); hence, the entire length of irrigation tubing need only be continuously driven at a rate so as to make one revolution about the central water supply pipe every eight days.
Hydraulically power driven rotary irrigation systems, which operate under the water pressure in the irrigation tubing may include a single power mover connected at the outer end of the tubing, or they may include a plurality of movers located at support carriage assemblies along the length of the tubing. When a single mover is used the tubing bends due to a drag on the support assemblies caused by rolling resistance between the ground and wheels on the carriage assemblies, so heavy and expensive tubing must be used to prevent the tubing from bending and collapsing.
When a plurality of power movers are spaced along a length of the tubing the outer mover must be designed to move at a greater rate than the inner movers. It is difficult to cause each of the movers to advance at the proper rate as the tubing moves in a circle about a fixed central water supply.